Page 289 - Fundamentals of Reservoir Engineering
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OILWELL TESTING 226
values of ∆p and ∆t can be used in this analysis. Russell recommends that plot should
be made only for values of ∆t measured after one hour of closed-in time.
C - TOO SMALL
p∆
1
1 −
C∆t
C - TOO LARGE
(psi)
log ∆t
Fig. 7.38 Russell plot for analysing the effects of afterflow
Having chosen the correct value of C. the slope of the straight line is measured
(m−psi/log cycle) and the formation kh value can be determined using the equation
162.6q B
µ
kh = o (7.78)
m
The skin factor can be calculated using the expression
p − p k
−
S = 1.151 wf(1 hr) wf − log 2 + 3.23 (7.79)
−
11/ C t ∆ φµ cr w
m
b) McKinley Analysis
To apply the McKinley method it is necessary to plot the pressure buildup in a special
manner and compare the resulting plot with so called "Type Curves" presented by
21
McKinley , as shown in fig. 7.39.
